Pesticide Residues in the Atmosphere - Pesticides: Evaluation of Environmental Pollution - page 218

Table 7.2 shows pesticide measurements from different sites around the world. It is
indicative of the current worldwide interest in ambient air monitoring of pesticides, but
it cannot be considered an exhaustive review of the measurements taken in recent years.
7.4.2 Pesticides in Rainwater
Precipitation samples are usually collected with wet-only precipitation collectors. In some
cases, the samples are adsorbed on-line on XAD-2 resin columns during each precipitation
event (Aulagnier et al. 2008). In other studies, solid phase extraction (SPE) cartridges are
used to prepare the sample for analysis (Bossil et al. 2002; Vogel et al. 2008). In the last few
years, solid phase microextraction (SPME) techniques have been developed for the sam-
pling of pesticides in rainwater (i.e., Sauret-Szczepanski et al. 2006; Scheyer et al. 2007b).
After the sample is treated, the extracts are analyzed by GC-MS or LC-MS.
In addition to the meteorological conditions and the geographical situation of the analyzed
sampling sites, the physicochemical properties of the pesticides are also very important for
rainwater sample analyses. For example, Scheyer et al. (2007b) observed that parathion-
methyl was detected episodically in Strasbourg, and its low Henry's law constant (9.6 × 10 −4
Pa m 3 /mol) together with its good solubility in water (60 mg/L) permitted a good washout
by precipitation. By contrast, alachlor, atrazine, and metolachlor were detected seasonally,
and their low Henry's law constants and high water solubility enhanced their presence in
rainwater, because pesticides with low Henry's law constants and high water solubility are
mainly present in the particle phase and can be easily deposited by precipitation.
Table 7.3 shows some examples of the measurements carried out during the last few
years. It is not an exhaustive data review, but, rather, it reflects the current interest and the
importance of this kind of measurement in relation to air quality issues.
7.4.3 Measurements of Persistent Organic Pollutants
During the last 40 years, a great number of pesticides in the group of persistent organic
pollutants (POPs) have been banned in North America and Europe. For example, in 2001
during the Stockholm Convention, more than 160 governments agreed to add lindane to
the list of POPs to be banned for agricultural usage during the following years, although
its use for pharmaceutical purposes was permitted until the end of 2015. Nevertheless,
compounds of this type have half-lives of more than 2 days in air (Pacheco Ferreira 2008)
and can move in the environment during long periods of time—depending on the half-life
time of each compound—due to winds, wet and/or dry deposition, etc.
Within the US Integrated Atmospheric Deposition Network, 24 organochlorine pesti-
cides classified as POPs have been measured since 1990 and evaluated to analyze their time
trends in the Great Lakes region (Venier and Hites 2010). Gas and particle phases together
with precipitation were sampled every year and analyzed using GC-MS. The authors
found that endosulfans showed the slowest decreasing rate, between 11 and 14 years. For
chlordane, they observed a halving time of around 6 years for the particle phase, 11 years
for the gas phase, and nearly 4 years for the precipitation. Although they could not find
any explanation for this great difference in the halving time for precipitation, they con-
cluded that their results were consistent with the fact that chlordane, although banned
in the United States in 1988, still had several reservoirs resulting from past uses, which
continue to contaminate the atmosphere. These authors also reported that lindane showed
the fastest decline rates in all phases, between 3 and 5 years, in comparison with the other
organochlorine pesticides.